This invention relates to lightweight structural members and more particularly to multiple layers of honeycomb, foam or similar lightweight material members bonded together for increased structural strength and improved bonding strength.
Structural uses of honeycomb and foam construction have been confined previously to single layers. Increased advantages of strength-per-weight, torsional strength, joining strength, impact strength and other advantages related to particular products, however, can be achieved with multiple layers of bonded honeycomb members. The aerospace industry is the most prolific user of honeycomb construction. There its often greater cost is compensated by essential strength-per-weight. Prior use of multiple honeycomb layers have been only at joints to join single honeycomb layers to other single layers or to other structural members of aircraft. The use of multiple layers for increased structural strength in addition to increased joining strength and decreased construction cost has not been recognized nor developed. U.S. patents describing joining methods with variations of multiple layers of honeycomb material include U.S. Pat. No. 4,671,470 granted to Jonas in June 1987; U.S. Pat. No. 4,395,450 granted to Whitener in July 1983; and U.S. Pat. No. 4,416,349 granted to Jacobs in November 1983. None of these employed multiple layers except to a limited extent at joints. They did not provide the strength of multiple layers throughout the structure and at the joints.
Other methods of joining honeycomb members have included variations of potted bolts such as described in U.S. Pat. No. 4,370,372 granted to Higgins in 1983; U.S. Pat. No. 4,052,202 granted to Fischer & Fischer in 1977; and U.S. Pat. No. 3,282,015 granted to Rohe et al. in 1966. Like the multiple layers only at joints, the potting methods provide only local strength and resulted in decrease of overall strength per weight.